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DoDecaHedron Light Fixtures #1: Nothing Went Right

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Blog entry by MarkTheFiddler posted 702 days ago 2020 reads 0 times favorited 13 comments Add to Favorites Watch
no previous part Part 1 of DoDecaHedron Light Fixtures series Part 2: It's actually looking OK »

I cut This way, That way, Upside down and Sideways. I thought I had it all down but nothing was making sense. I truly made an impressive pile of kindling.

Then, I thought I had it. I tried to assemble and discovered another error in my logic.

Here is a sample:

That’s not bad for practice but I soon discovered the error of my ways.

The angle where the two boards are joined was cut at 13.28 degrees or my absolute best estimate. My machines are just not that precise. Why 13.28? It’s 58.28 degrees minus 45 degrees. 58.28 degrees was specified in a question I asked about a month ago. So far, I don’t see anything wrong with that angle.

Here’s another shot of that end.

I also double mitered the end pieces. 36 for the pentagon angle and 13.28 for the inside angle. As it turns out, you only want the 36 degrees there. When you try to put the pieces together, the second miter cut messes up the angle. Here’s a shot of 3 sides of the pentagon.

If you will notice, the angle is not quite right. Sides 5 and 6 won’t fit.

I know what to do tomorrow. There won’t be a bunch of experimental cutting. If I’m lucky, I’ll be able to connect 5 pentagons. I’d be a lot less dry about this If I had anything to show for my efforts. At least I have a little knowledge. Wish me luck.

-- Thanks for all the lessons!



13 comments so far

View KOVA's profile

KOVA

1308 posts in 974 days


#1 posted 702 days ago

SUERTE AMIGO ;-0

-- KOVA, EL CARPINTERO DEL PUEBLO https://www.facebook.com/pages/El-Carpintero-Del-Pueblo/148976618479733

View lanwater's profile

lanwater

3072 posts in 1530 days


#2 posted 702 days ago

Why not assemble each pentagon first then cut all the dihedral angle all the same (58.28) then proceed to the final pentagon to pentagon glue up?

You will end up with the same results but I think there is less room for errors when you assemble with one whole polyhedron.

90-58.28 for the complemantary angle no?

Here is a link with similar projects for ideas: http://www.toshen.com/woodworking-reviews01.htm

best of luck.

-- Abbas, Castro Valley, CA

View CharlieM1958's profile

CharlieM1958

15639 posts in 2814 days


#3 posted 702 days ago

Wish I could help, but all this math is too much for a liberal arts major. :-)

-- Charlie M. "Woodworking - patience = firewood"

View MarkTheFiddler's profile (online now)

MarkTheFiddler

1723 posts in 784 days


#4 posted 702 days ago

Gracias Kova!

Lanwater,

Thanks for the resource. I see why you recommend building the individual pentagons then cutting the angle. It makes a lot of sense when gluing the individual pentagons. It’s also an easy-ish chore to glue the pentagons together. I liked the simple prospect of cutting a single miter angle down the length of the table saw. It sure makes glue up difficult though.

The next time I get a window of time for cutting, I’ll try the miter after i build a pentagon.

-- Thanks for all the lessons!

View MarkTheFiddler's profile (online now)

MarkTheFiddler

1723 posts in 784 days


#5 posted 702 days ago

Lanwater,
I forgot to say, I really appreciate yor time!

Hey Charles,
This math may kill me too.

-- Thanks for all the lessons!

View lanwater's profile

lanwater

3072 posts in 1530 days


#6 posted 701 days ago

Anytime.

If you are cutting on the table saw, build a sled for cutting the dihedral angles; it helps align and it keeps your finger away from the blade.

It’s an exiting project. I had a variation of it on my list but never got to it.

-- Abbas, Castro Valley, CA

View MarkTheFiddler's profile (online now)

MarkTheFiddler

1723 posts in 784 days


#7 posted 701 days ago

LanWater,

I saw your sled. It makes a lot of sense. Before I realized you actually made a half sled, I was going to put a jig on piece of plywood and use the fence.

Clever concept with the roll. I’m considering it because I’m making 3 light fixtures. That’s 12 pentagons per fixture, 60 segments per fixture, 180 segments for 3 lights. Why oh why do I get myself into these tedious projects?

-- Thanks for all the lessons!

View CessnaPilotBarry's profile (online now)

CessnaPilotBarry

877 posts in 706 days


#8 posted 701 days ago

Why not divide the project in sections, in an MDF prototype or on paper, and take direct bevel settings to set the tool angles? Even if you design the item in Sketchup, have it printed in full size three views, use them to set bevel gauges.

This is very common in chair making. Not many successful chair makers will bother to calculate angle settings to the right of a decimal point.

If you want to reproduce the item, cut setup blocks after each successful part is made. Use the blocks to set the tools next time.

-- It's all good, if it's wood...

View CessnaPilotBarry's profile (online now)

CessnaPilotBarry

877 posts in 706 days


#9 posted 701 days ago

If you’re a FWW subscriber, Steve Brown wrote about a dirt simple way to do screwy compound angle cuts, and his “magic block”.

http://www.finewoodworking.com/SkillsAndTechniques/SkillsAndTechniquesPDF.aspx?id=2807

The Magic Block is simply a solid model of the shape you wish to create.

-- It's all good, if it's wood...

View MarkTheFiddler's profile (online now)

MarkTheFiddler

1723 posts in 784 days


#10 posted 700 days ago

Hey Barry!

I certainly appreciate the advice. I’m with you 100% on keeping templates and prototypes. I’m actually trying this out some very inexpensive Pine I scored. The magic block sounds very interesting. Thanks for the lead. I’ll follow up on it.

-- Thanks for all the lessons!

View MarkTheFiddler's profile (online now)

MarkTheFiddler

1723 posts in 784 days


#11 posted 688 days ago

Do you know what is wrong with being absolutely positive that you know exactly what you are doing? It takes LONGER to find out you are absolutely wrong. I managed to make more kindling today – but I was close – so I thought I could build the prototype anyway with a little adjustment here and a little tweak there.

That my friends is what I call a waste of LIFE!

Well almost a waste. I learned a lot of lessons, the hard way, Once again.
I’m going to do exactly what LanWater did next time.

My bevel angle was all wrong by the way. I believe I need 29.smidgeon. That happens to be half of the 59.24 angle I was told about. Ignore all my other angle comments.

Can someone confirm my bevel? (Some questions just sound weird).

-- Thanks for all the lessons!

View MarkTheFiddler's profile (online now)

MarkTheFiddler

1723 posts in 784 days


#12 posted 687 days ago

I tried again today. The thing is actually coming together. Although, there are gaps and uneven cuts, I’m going to keep this one and give the dodecahedrons a rest. I’m not how much is because of my poor quality tools or my amateur skills. Still, I learned a lot. I’ll try to build a better one in 6 months or so.

I’ll post this fixture as a project after I do the unthinkable. I’m going to use wood filler. Gasp! Isn’t wood filler illegal at lumber jocks?

-- Thanks for all the lessons!

View MarkTheFiddler's profile (online now)

MarkTheFiddler

1723 posts in 784 days


#13 posted 686 days ago

Well, I thought the the thing was going to look like hell. However, it looks 10 times better today than yesterday. I know sanding should not be the solution for bad uneven joints, but this little project is turning out to be useable. It may possibly turn out to be good looking. I won’t hold my breath. I still have some seams that I can’t close without filler.

-- Thanks for all the lessons!

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